Question

7 pens cost ₹ 36. What’s the cost of 21 pens ?

Answer 1

Hint: In the given equation, there is only one unknown value. Let us consider the cost of pen be \[x\] and then proceed as the question says. First we need to find the cost of \[1\] pen.

Complete step-by-step solution:
Now, We need the cost of \[1\] pen. We have already considered the cost of pen as \[x\]
Given, cost of \[7\ \] pens = \[36\]
ie). \[7x = 36\]
 \[x = \dfrac{36}{7}\]
Cost of \[1\] pen=Rs.\[\dfrac{36}{7}\]
Now we need to find the cost of \[21\] pens,
Cost of \[21\] pens\[\ = \ 21 \times \dfrac{36}{7}\]
By dividing \[21\] by \[7\] ,
We get,
=\[\ 3 \times 36\]
By multiplying, we get the cost of \[21\] pens
Cost of \[21\] pens = \[108\]
Final answer :
The cost of \[21\] pens = \[108\]
Additional information: Any linear calculations requiring one or more than one variable that can be solved with the help of linear equations.A linear equation can be written in many different ways. In the case of one variable, there will be one solution But in the case of two variables, there will be one solution but we need to form two equations.

Note: In some cases if we have to find \[2\] unknown variables, we have to form \[2\] linear equations with \[2\] variables. Similarly if we have \[3\] unknown variables, we have to form \[3\] linear equations with \[3\] variables. For these equations we use the traditional method of solving the linear equations.